1. Field of the Invention
The present general inventive concept relates to a display apparatus to detect a letter-box boundary and a method of displaying an image using the same, and more particularly, to a display apparatus to detect a letter-box boundary using a run-length of consecutive pixels of a specific color and a method of displaying an image using the same.
2. Description of the Related Art
A letter-box refers to a blank space positioned at upper and lower edges of an area in which an image is displayed, i.e., a non-signal area. In a case in which a letter-box area exists in an input image, an output image is not displayed in the letter-box area but only in an image area other than the letter-box area. Accordingly, a burning effect occurs when displaying the output image.
In a case in which an input image having a letter-box is input to a display apparatus, a size of the image is transformed so that a size of an image area in which the image is displayed except the letter-box area is suitable for a size of a screen of the display apparatus so as to display the image on the screen. This is called auto-wide. A process of detecting a letter-box boundary and dividing a letter-box area and a substantial image area is required during an auto-wide operation.
FIG. 1 is a block diagram illustrating a conventional display apparatus for detecting a letter-box boundary. Referring to FIG. 1, the conventional display apparatus includes an edge determiner 101, a counter 103, a position storage 105, and an image area determiner 107.
The edge determiner 101 determines whether an edge exists in an input image, using luminance Y and chroma C of the input image. The edge determiner 101 determines an area including a sharply decreasing or increasing pixel average value of a predetermined line of the input image as the edge.
The counter 103 counts a number of lines determined to be edges by the edge determiner 101.
If the number of lines determined to be edges is greater than or equal to a predetermined number, the position storage 105 determines the edges to be potential boundaries between a letter-box area and an image area in which an image is substantially displayed and then stores information regarding positions of the lines determined to be the edges. The lines of the input image determined to be the edges are highly likely to be the boundaries between the letter-box area and the image area. Thus, if a predetermined number of edges of sequentially input images are detected at the same positions as the stored position information, the positions may be determined as boundaries of the letter-box area.
The image area determiner 107 determines whether a line determined as an edge is a boundary of the letter-box area, using the information regarding the positions of the lines determined to be the edges stored in the position storage 105. If a position of a line determined to be an edge is detected a predetermined number of times or more, the image area determiner 107 determines the position of the line to be a boundary of the letter-box area. In other words, an area on one side of the line determined to be the boundary is determined to be the letter-box area, and an area on the other side of the line is determined to be the image area.
FIG. 2 is a view illustrating a conventional method of detecting a letter-box area. Referring to FIGS. 1 and 2, in the conventional method, if edges are detected at Nth and N−1th lines of an input image, the counter 103 counts a number of edges detected at the Nth and N−1th lines of sequentially input images, and the position storage 105 stores information regarding positions of the Nth and N−1th lines.
If edges are detected a predetermined number of times or more at the Nth and N−1th lines of the images sequentially input following the input image after the edges are detected at the Nth and N−1th lines of the input image, the image area determiner 107 determines the Nth and N−1th lines to be boundaries of a letter-box area existing in each of the input images.
However, in the conventional method of detecting a letter-box area using detection of an edge between consecutive lines, if a Computer Graphics Interface (CGI), such as a caption or a logo, is positioned in the letter-box area, an edge is not detected at a boundary of the letter-box area due to the caption or the logo. Thus, the boundary of the letter-box area may not be accurately detected.
If a size of an image area except the detected letter-box area is changed to be suitable for a size of a screen of the display apparatus, the size of the image area may be changed several times due to an inaccurate detection of the boundary of the letter-box area. In other words, a position of a predetermined line of an input image may not be determined as a boundary of a letter-box area due to an inaccurate detection of the letter-box area. Thus, the size of the image area may be frequently changed during displaying of an image. The frequent change of the size of the image area may deteriorate temporal image quality.